The present invention is an improvement over my co-pending application, Ser. No. 752,084, filed Dec. 20, 1976, entitled now U.S. Pat. No. 4,094,175, patented June 13, 1978, "Internal Tumbler Lock Key Change System."
1. Field of the Invention
The present invention relates to a key-operated pin tumbler lock and, more particularly, to such a lock having vastly expanded capacity for increasing the number of unique lock changes.
2. Description of the Prior Art
Key operated locks are adapted to permit their operations by different combinations and uniquely configured keys therefor. As the number of combinations increase, the number of uniquely configured keys therefor increase, albeit not in direct proportion. It is accordingly possible to secure a large number of enclosures without use of the same combinations. For example, for a conventional tumbler pin cylinder lock utilizing a five pin system with a single bottom pin and a single top pin in each of the five pin chambers, the lock combination is one. When master pins are added to a chamber, for x master pins added to n chambers, the lock combination may be expressed by the formula: (x+1).sup.n. However, as the number of master pins increase, it becomes easier to pick the lock. Therefore, it is preferable to utilize not more than two master pins per chamber. For a system based upon a maximum of two master pins and one bottom pin per chamber, the number of combination is 3.sup.5, or 243 combinations.
Of these 243 combinations, all may be operated by a single key, called a master key. Some keys in this number of combinations bypass others, but 51 of them are distinct from all others. Such a system may be useful in such buildings as apartment houses and office buildings. In other buildings, however, it may be desireable to have more than one master key, such as in a hotel, where there may be one master key per floor and one grand master key for all floors. In such a situation, for a building requiring 2-5 master keys, and one grand master key, the number of unique distinct operating keys is reduced to 13. In a like manner, for one great grand master key, there would be 2 grand master keys, 10 master keys, and 7-8 distinct operating keys. From the above, it is apparent that there are limitations when it is desired to utilize master, grand master and great grand master key levels.
Added to this limitation, tumbler pin cylinder locks have been devised so that their combinations may be changed for use with different keys, such as may be required in buildings with many offices or rooms, occupied at different times by various tenants, as in hotels, apartments and office buildings. In prior art locks for such systems, changes were usually effected by removing the lock from its emplacement to make the changes.